An alternative to 6080's / 6AS7G; The Telefunken ED8000 single triode. Started looking for these last year. They're hard to source and you need two to replace a single 6080. From the datasheet they look very promising. With an internal resistance of only 220 Ohm and a transconductance of 16ma/V it's a perfect candidate for the OTL Bottlehead Crack. Beware you need to wire your own adapter (I used and rewired a CV4079 adapter for mine).
How does it sound? It's a typical Telefunken. Clean, clear; even from top to bottom; bringing out lots of details. Unfortunately they don't have the biggest of soundstage. Nor the most romantic sound. For me personally the GEC CV4079's get the preference. Pair ED8000 with a Telefunken ECC82 for a hard hitting bass but be warned for some sharp and sibilant high's. However they pair perfectly with slightly rolled off drivers.
Here's a pair pictured with Visseaux type 76 drivers.